The present invention relates to ionic electrolytes useful in connection with electrolytic capacitors and certain other energy storage devices. More particularly it relates to hydroxy terminated organosilicon electrolytes that are particularly useful in an aqueous electrolytic capacitor environment.
Over the past decade our laboratory has been developing organosilicon based electrolytes for energy storage applications. Various of these organ silicon compounds have low vapor pressure, high flash point, and withstand high operating voltages.
For example, we previously reported the synthesis of some alkyl terminated trimethylsilyl oligoethylene glycol ethers in L. Zhang et al., Highly Conductive Trimethylsilyl Oligo(ethylene oxide) Electrolytes For Energy Storage Applications, 18 J. Mater. Chem. 3713-3717 (2008). These materials had high ionic conductivity, good electrochemical stability, and good cycling performance when used as electrolyte solvents in lithium-ion cells. However, they were susceptible to being hydrolyzed under some conditions.
We also reported in U.S. patent application publication 2007/0065728 the concept of placing an alkyl spacer in such alkyl terminated compounds between the trimethylsilyl group and the remainder of the molecule. This helped the molecule resist hydrolysis. However, the compounds still did not achieve desired performance in certain environments.
One reason is that a variety of electrolytic capacitors use water to repair aluminum defects. See generally descriptions of electrolytic capacitors in U.S. Pat. No. 6,058,006. Conventional aluminum electrolytic capacitors sometimes use an electrolyte mix of gamma-butyrolactone, diethylene glycol, triethylammonium azelaate, and water. To achieve the advantages of our alkyl terminated organosilicon compounds with this type of capacitor there were attempts to replace the gamma-butyrolactone and diethylene glycol with them. However, alkyl terminated organosilicon electrolytes typically had performance issues in this environment.
In U. Yoon et al., Efficient And Regioselective Photocyclization Reactions Of N—[(ω-Trimethylsilylmethoxy)Polyoxalkyl]Phthalimides To Azacrown Ethers, 41 Heterocycles 2665-2682 (1995) the authors reported the synthesis of Me3Si—CH2OCH2CH2OCH2CH2OCH2CH2—OH, Me3Si—CH2OCH2CH2OCH2CH2—OH and Me3Si—CH2OCH2CH2OCH2CH2OCH2CH2—OH (and various related compounds) as intermediates in the production of azacrown ethers. Apart from the fact that their syntheses required use of relatively expensive Me3Si—CH2I, there was no suggestion in their article to use these intermediates as electrolytes.
There is therefore a need for additional improvements with respect to organosilicon electrolytes for energy storage devices, particularly improvements relating to compatibility with water environments.